Fuses are a type of programmable ROM that are often utilized to store chip-specific information such as a stock-keeping-unit (SKU) configuration, calibration parameters, chip ID, RAM repair, etc. Earlier generations of chips used dedicated fuse bits in a fuse macro to store a particular feature. Automated Test Equipment (ATE) program would then be used to burn the fuses to select a feature.
Using the dedicated fuse bits had advantages with the ATE and in operations of the manufacturer since it was easy to convert a chip to a given SKU by burning specific bits in a fuse macro. The main disadvantage, however, was the lack of re-programmability; once a particular configuration for the chip was set, it could not be changed. Thus, human and programming errors could not be corrected and could lead to inventory backlogs and waste when errors occurred on a large scale. Accordingly, changes, such as fuse-based RAM repair, could not be supported in a flexible fashion under a fixed programming scheme.